1. Field of the Invention
This invention relates to a cooling device for heated steel plates and more particularly to an improvement of a nozzle header for cooling upper surfaces of plate materials.
2. Description of the Prior Art
It has been well known to improve steel properties such as mechanical properties by cooling the heated steel at a determined cooling speed. A continuous heat treatment method for cooling moving steel plates serves to improve productivity in a steel manufacturing line. Particularly, the continuous heat treatment of heated steel plates immediately after being rolled in a rolling mill line can dispense with heating of the steel plates for the heat treatment to provide great merits in economy of energy and improvement of productivity, and simultaneously can possibly improve the material quality by the heat treatment in conjunction with the working in rolling. Recently, the heat treatment in the rolling mill line has been earnestly investigated, in order to obtain a cooling device easily controlled and having an adjustable wide cooling performance.
In general, cooling devices for heated steel plates will encounter a difficulty in removing cooling water on the steel plates to be cooled. The remaining cooling water frequently forms a water layer more than 50-60 mm in depth. In order to effectively cool the upper surfaces of the steel plate, therefore, the cooling water should be strongly penetrated into such a thick water layer so as to directly reach the surfaces of the plates or the remaining water on the plates should be violently stirred or agitated by the cooling water jetted from the cooling devices.
On the other hand, the cooling device for cooling heated steel plates, particularly cooling surfaces of the plates should be arranged as high as possible above the plates in order to avoid an occurrence of scratch on the plates or damage of the cooling device when it moves above the plates, due to a contact therebetween owing to, for example, a deformation of the plates. Accordingly, it is necessary to increase a concentric velocity or density of the cooling water jetting from the cooling device at the surface of the plate for the purpose of fulfiling the condition of the strong penetration or violent agitation required for the cooling device as above described.
Moreover, it is desired for the cooling device to be able to stop jetting cooling water instantaneously, when required, in order to control the temperature at the end of cooling to obtain high quality steel plates.
A nozzle header 60 as shown in FIG. 1 has been proposed. However, it cannot stop jetting cooling water from the header if required, because a volume S.sub.1 ' of the cooling water in the header 60 above an upper end of a nozzle 4' is fairly large, which would delay a complete stoppage of the cooling water after the water supply to the header 60 has been shut off. This header 60, moreover, cannot achieve uniform cooling of plates because the cooling water exclusively flows in its longitudinal direction so as to be unequally distributed into nozzles.